Proper packaging of micro components is important to ensure the integrity of the signals to and from the micro components and often determines the overall cost and size of the assembly.
For example, MEMS devices, such as accelerometers and other inertial sensors, have found applications in various consumer products including laptop computers, cell phones and handheld computers. In some applications, the MEMS device is fabricated on the same die as the signal process circuitry. For example, BiCMOS circuit fabrication processes may be integrated with a surface micromachined MEMS process. Integrating the micro component with the circuitry can facilitate signal amplification and signal processing.
The overall process of manufacturing a package that encapsulates such an integrated MEMS device may include the following steps: (i) fabrication of an integrated MEMS device; (ii) a wafer capping process for the MEMS device; and (iii) assembly of the capped MEMS device in the package. One advantage of capping the MEMS device prior to assembly is that it can reduce the complexity of the subsequent dicing operation. Another advantage is that the cap can protect the MEMS device when the die is attached, for example, to a lead frame. A schematic cross-section of a package for a capped sensor die that includes a MEMS device is illustrated in FIG. 1 and is described in further detail in Felton et al., “Chip Scale Packaging of a MEMS Accelerometer,” 2004 Electronic Components and Technology Conference, IEEE, pp. 869-873 (2004).
An important factor for handheld consumer products such as those mentioned above is the size and weight of the package. Although the techniques described in the foregoing article apparently result in a relatively small package, they require the use of wire bonding for the electrical connections between the lead frame and the die for the MEMS device. The overall footprint of the package, including the electrical connections to the lead frame, is larger than the footprint of the sensor die. For some applications, it may be desirable to have a smaller footprint.